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premium price they may demand because of their ability to troubleshoot and get equipment back on line efficiently and effectively.
System Components and Controls Knowledge and System Components and Controls Knowledge and Expertise.
Expertise.
• Treatment, accessory, and ancillary equipment— Does the service provider have the expertise to perform refrigeration and other work on dryers and related equipment? Is the service provider capable of servicing the types of filters, drains, distribution and point-of-use equipment found in your facility? • System controls—Does the service provider have the
diagnostic and technical controls capability to determine how to optimize your existing control configuration and make recommendations for improvements? Can they help network compressors together or remotely monitor, if necessary? Advanced controls can save energy as well as improve reliability through automatic start and stop, as well as turning compressors off that can then serve as back-ups. Advance warning through remote monitoring may help identify a problem before it turns into a major shutdown.
Company Capabilities.
Company Capabilities.Ask about the standards of performance that the prospective service provider has established for:
• Emergency service response • Parts shipments
• Other factors which may influence your decision, such as:
– Installation capabilities internally or through a mechanical contractor – Emergency rental fleet availab ility—electric
or portable diesel driven.
• Your company may request information on the service provider’s:
– Financial stab ility – Insurance coverage
– Compliance with specific government regulations or those of your company.
Service Facilities.
Service Facilities.Visit the facilities of two or three service providers under consideration to see first hand the type of repair shop and parts warehouse with which you will be dealing.
Important aspects of a basic compressed air system audit are discussed below.
System Issues System Issues
System issues go beyond examining the performance of an individual compressed air system component and, instead, examine how components on both the supply and demand sides of the system interact. Auditors typically address a number of systems issues. These are discussed below, and many are addressed in more detail in other compressed air systems fact sheets.
Level of Air Treatment.
Level of Air Treatment.The auditor typically examines the compressed air applications and determines the appropriate level of air treatment required for proper operation of the equipment. Actual air quality levels are then measured. If the air is not being treated enough, alternative treatment strategies are recommended. If the air is being overtreated (an indication of energy being wasted), recommendations are made to modify the system. In some cases, only certain end-use equip- ment requires highly treated air, and the auditor may recommend a system that allows for different treatment levels at different points in the system.
Leaks.
Leaks.The auditor should identify and quantify leaks in the system and recommend a leak management program.
Pressure Levels.
Pressure Levels.An auditor also typically determines the lowest possible pressure level required to operate production equipment effectively. In many cases, system pressure can be lowered, thereby saving energy. Most systems have one or more critical applications that determine the minimum acceptable pressure in the system. In some cases, the application of dedicated storage or differential reduction on the critical applications will allow a reduction in overall system pressure.
Controls.
Controls.The existing control system is evaluated to determine if it is appropriate for the system demand profile. Performance gains available from operating the system in a different mode or using an alternative control strategy should be estimated.
Heat Recovery.
Heat Recovery.Auditors will identify potential applications for the use of heat recovery, if it is not already being used.
Demand-Side Issues Demand-Side Issues
The demand side of the system refers to how compressed air is actually used in the plant.Distribution System.Distribution System.The overall layout of the distribution system (piping) is examined. Pressure drop and efficiency are measured or estimated, and the effectiveness of the condensate removal system is
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evaluated. Simple changes that can enhance system performance are suggested if appropriate.
Load Profile.
Load Profile.Auditors typically estimate the compressed air load profile in terms of how the demand in cfm changes over time. A facility with a varying load profile will likely benefit from advanced control strategies. A facility with short periods of heavy demand may benefit from implementing storage options.
To establish the load profile, an auditor will measure system flow and pressure across the system under different demand conditions, while observing the loading effect on the existing compressors. This may require a number of measurements over a 24-hour period (or even several days) if demand varies significantly over time. Auditors may use data logging equipment to obtain both demand and power consumption profiles.
End-Use Equipment.
End-Use Equipment.The equipment and processes that use compressed air will also be examined. In some cases, recommendations, such as specifying equipment that operates at a lower pressure, will be made. An auditor may also recommend replacing existing compressed air-powered equipment with equipment that uses a source of energy other than compressed air. (See the fact sheet titled Potentially Inappropriate Uses of Compressed Air.) Critical pressure
applications are examined in detail. Local storage and other modifications may be recommended.
Supply-Side Issues Supply-Side Issues
The supply side refers to how the compressed air is generated and treated.
Compressor Package.
Compressor Package.The compressors are evaluated in terms of appropriateness for the application and general appearance and condition. Compressor efficiency is usually estimated based on manufacturer- supplied data, corrected to site conditions. The installation is also evaluated in terms of its location, connection to cooling water, and ventilation. A general appraisal and any recommendations for alternative systems are also made.
Filters.
Filters.Filters are examined for cleanliness and suitability for the application. Pressure drop across the filters is measured to estimate energy losses from the filter. A maintenance schedule for changing the filters, and possibly higher performance filters, may be recommended.
Aftercooler.
Aftercooler.Aftercooler and separator efficiency,
cooling effectiveness, and condensate separation effectiveness are all measured and evaluated, and feasible modifications or alternative systems are recommended.
Dryer.
Dryer.Dryer appropriateness is assessed based on the facility’s end-use applications. Dryer size, pressure drop, and efficiency are measured and evaluated. Modifications and replacements are recommended if needed.
Automatic Drains.
Automatic Drains.Location, application, and effectiveness of both supply-side and demand-side drains are evaluated and alternatives recommended if necessary.
Air Receiver/Storage.
Air Receiver/Storage.The effectiveness of the receiver tank is evaluated in terms of location and size, and the receiver drain trap is examined to see if it is operating properly. Storage solutions to control demand events should also be investigated.
More Comprehensive Evaluations More Comprehensive Evaluations
A comprehensive evaluation may also include extensive measurements and analysis of supply and demand interactions. Some auditors will also prepare a detailed systems flow diagram. A financial evaluation may also be performed, including current and proposed costs after retrofits are taken.
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12–Compressed Air System Economics and Selling Projects to Management 12–Compressed Air System Economics and Selling Projects to Management
Delivering compressed air to a manufacturing facility is an expensive operation. Delivery requires costly equipment that consumes significant amounts of electricity and needs frequent maintenance. In spite of this, many facilities have no idea how much their compressed air systems cost on an annual basis, or how much money they could save by improving the performance of these systems.
Costs are by far the largest expense of owning and operating a compressed air system. The initial cost for a 100-hp compressor is $30,000 to $50,000, depending on the type of compressor and manufacturer, while annual electricity charges for the same system can reach $50,000. Added to this are annual maintenance costs, which can be 10 percent or more of the initial cost of the system.
This fact sheet shows a simple calculation to estimate annual electricity costs and a more accurate calculation requiring electrical measurements.
Calculating Electricity Costs Calculating Electricity Costs
Full-Load Operation.
Full-Load Operation.Even if an air compressor is not separately metered, estimating annual electricity cost is simple. For more analysis techniques, see the AIRMaster+ software referenced in the Resource and Tools section, and/or call the Compressed Air Challenge®number listed in the Directory section.
A Simple Calculation.
A Simple Calculation.The following data is needed for a quick calculation of electricity costs for a compressor operating at full-load.
• Compressor motor nameplate rating (bhp) • Motor nameplate efficiency (or an estimate of
efficiency)
• Annual hours of operation (hours/year) • Cost of electricity in dollars per kilowatt-hour
($/kWh).
Annual electricity costs can be calculated by inserting this information into the equation as follows:
This equation assumes the electric motor driving the compressor is 90 percent efficient (the 90 in the 1/0.90 factor). Newer energy-efficient motors have even higher efficiencies, especially since the Energy Policy Act minimum motor efficiency levels went into effect in late 1997. If the system uses an older motor that has been rewound several times, or has a smaller motor, 80 percent efficiency (or the motor nameplate efficiency rating) should be used. For a more accurate analysis, add the horsepower ratings for the parasitic loads from any auxiliary motors to the compressor motor rating.
It should be noted that the common practice in the industry is to apply motors having a 15 percent continuous service factor and to use about two-thirds of this service factor. This means that a motor having a nominal nameplate rating of 100 hp may, in fact, be loaded to 110 bhp at compressor full capacity and pressure. This may not be expressed in the manufac- turer’s sales literature, however, engineering data sheets for the specific compressor should be consulted. If the motor is running into the service factor, the higher horsepower estimate should be used instead of the nameplate horsepower rating.